MOS transistors, such as, for example, MOSFETs (Metal Oxide Semiconductor Field-Effect Transistors) or IGBTs (Insulated Gate Bipolar Transistors) are increasingly employed as electronic switches for switching electrical loads. As is known, MOS transistors have a control capacitance or gate capacitance which must be charged for switching on the MOS transistor, i.e. for transferring the MOS transistor into its conducting state, and which capacitance must be discharged for switching off the MOS transistor, i.e. for transferring the transistor into its non-conducting/blocking state. The speed at which this gate capacitance is charged and discharged is determined by the switching behavior of the MOS transistor. Consequently the slope of the switching edges of electrical signals applied across the MOS transistor or across a load connected in series to the MOS transistor. Such electrical signal is a current through the transistor or the load, or a voltage across the load or the transistor and is dependent on the control capacitance. The charging or discharging speed is a function of the amplitude of a charge or discharge current and of the capacitance value of the control capacitance.
The slope of these switching edges fundamentally determines the electromagnetic interference during a switching operation. One method reducing the electromagnetic interference during a switching operation is to “flatten” the switching edges through an appropriate selection of the charge and discharge current.
The value of the control capacitance of a MOS transistor which has a significant effect on the slope of the switching edges is subject to fabrication-related fluctuations. The slope of the switching edges can as a result vary from transistor to transistor given identical charging and discharging currents.